The invention relates to methods for producing clean coal of reduced sulfur content and more particularly to a method for the explosive comminution of coal.
Coal remains a major energy resource but much of the coal cannot be used economically because of its high sulfur content. The sulfur in coal combustion products may be a major contributor to acid rain.
Sulfur is contained in coal in organic or inorganic form. The organic sulfur is chemically bonded into the coal matrix while the inorganic sulfur occurs mainly as pyrite (FeS.sub.2) mixed with other inorganic minerals. During combustion, most of the sulfur is released as sulfur dioxide (SO.sub.2) which forms sulfuric acid from reaction with atmospheric moisture.
There are various approaches for limiting the discharge of sulfuric acid from coal combustion processes. The sulfur can be removed from the coal prior to combustion. It can be removed during the combustion stage or from the effluent gases. The present invention addresses this problem by removing sulfur and other mineral matter prior to use of coal.
Representative prior processes in pre-treatment of coal include those that employ explosive comminution as described in U.S. Pat. Nos. 4,313,737 and 4,421,722, both to Massey et al. A process of this type generally is most effective in the removal of pyritic sulfur and other minerals from comminuted coal. Consequently, these processes are limited in the fraction of sulfur that can be removed.
In other efforts, coal has been treated with molten alkaline in an effort to remove both the organic and inorganic sulfur. Although high proportions of this sulfur can be removed by this method, large quantities of molten alkaline, up to 10 times the weight of the coal in prosess, are required.
Therefore, in view of the above discussion, it is an object of the present invention to provide an improved process for removing objectionable materials from coal.
It is a further objective to provide a clean coal process in which a high proportion of sulfur is removed.
It is also an object of this invention to provide a process for removing sulfur from coal and other carbonaceous material wherein the material is comminuted to a finely divided powder.